Neck Relief and String Hight for Low Tunings?

Hi everyone,

I'm currently learning how to do my own guitar setups and have a few questions.

My guitar is a 24.75" Les Paul tuned to Drop A#, with a .068 on the lowest string. Since switching to the heavier gauge, I've been getting some string buzz and I'm trying to dial in the setup properly.

When checking neck relief, what clearance should I aim for around the 7th–9th fret when fretting the string at the 1st and 17th frets?

Once the relief is set correctly, what action would you recommend at the 12th fret for the low and high E strings?

I mainly play metal and prefer reasonably low action, but I'd like to avoid excessive fret buzz.

Right now, with the string fretted at the 1st and 17th frets, I have roughly business-card thickness of relief at the 8th fret. My low string measures about 3 mm (0.118") at the 12th fret, which seems quite high to me. The strange thing is that my bridge is already adjusted as low as it can go.

Does this suggest an issue with neck angle, fret height, nut slot height, or something else I'm overlooking? One more thing: when I installed the heavier strings, I widened the nut slots myself using cut-off pieces of guitar strings as makeshift nut files. The strings seem to sit properly in the slots, but I'm wondering if I may have introduced an issue there.

Thanks!